Abstract: The effect of different concentrations of CO₂ on the reproductive growth of Pleurotus lucidum is studied by controlling environmental condition in this paper．The upper limit critical CO₂ concentration in the normal differentiation of fruit-body was lO0umol／L After the fruit-body formation，the pileus enlargement was significantly inhibited and stipe elongation was significantly improved with increasing CO₂ concentration；for attaining excellent quality fruit-body of P．1ucidum，the range of CO₂ concentration in environment was under 35umol／L．